Binding of spermidine and putrescine to energized liver mitochondria

The binding of spermidine and putrescine to mitochondrial membranes was stu died by applying a thermodynamic model of ligand-receptor interactions deve loped both for equilibrium and far-from-equilibrium binding processes (V. D i Note, L. Dalla Via, A. Toninello, and M. Vidali Macromol. Theory Simul. 5 , 165-181, 1996). Results demonstrate the presence of two monocoordinated b inding sites (S-1 and S-2) for spermidine and one monocoordinated binding s ite (S-2) for putrescine, all exhibiting high capacity and low affinity. It is proposed that differences in the polyamines' flexibility and hydrophili city perhaps contributes to the observed variations in their interactions w ith the two sites. A comparison of the binding parameters of these polyamin es with those of spermine reveals differences in the specific function of t he S-1 and S-2 sites, identified in studies of spermine binding (L. Dalla V ia, V. Ri Note, D. Siliprandi, and A. Toninello Biochim. Biophys. Acta 1284 , 247-252, 1996), (C) 1999 Academic Press.